Im a bit sad to say in the least, I had saw this concept a while back in hopes you were gonna post progress as you went along......
The overall design based from your concepts to final presentation lacks in all regards
a few things that would have helped
That fur you kinda etched in kept it flat, or kept a shader on it to make it transmit more smoother
The posture of your character is so extremely ridged , even though humanoid has no character to it , just look like a plank standing straight
his face is creepy but its due to afew reasons, mainly on the front view of your character his eyes have were shadowing where the eyeballs themself are just floating in nothing
from the side view (based on your drawings) the skull was WAY more defined were as your 3d it again lacks.
shoe design I like no real complaints there
Glove design reminds me of kingdom hearts Im not a fan of the flesh fingers sticking out, but I suppose it could grow on me if the gloves were designed a bit more with details
having the muscles on this guy is fine but heres the thing
sonic is fast
he runs fast
fastest thing alive
Ever watch the saturday morning show you should know that just by the theme song
so tell me why is his ABS SO DEFINED but his legs are just semi defined?
Does sonic run Stomach first into shit?
he RUNS with his legs , he KICKS and spins with his back
Things that would have given it more character legs being more defined and OBVIOUSLY bigger (if your going for that kinda more detailed/ realistic vibe of sonic)
ok lets now think again other notable things with sonic
he attack how?
Quills on his back in a ball right?
Key word there "Back"
His back muscles / back frame would obviously would be wider wouldnt they?
Again more things Im trying to point out to hopefully help you evolve this character more
Im a fan of sonic/megaman/old school games
So I love to see redesigns or tribute models
I really think you should take this model back to concept really define your concept and start in your base mesh again and sculpt nicely
look into shaders that can render fur nicely (Example sonic unleashed had a type of fur shader for night werhog sonic)
Other shades similar to this were ones used for viva pinata
There tons to improve on , please take all my critics/ personal opinions with a grain of salt! But take grains of that salt to make your dish more favorable